U.S. patent application number 12/585617 was filed with the patent office on 2010-04-15 for pixel and organic light emitting display device using the same.
This patent application is currently assigned to SAMSUNG Mobile Display CO., LTD. Invention is credited to Do-Ik Kim, Wang-Jo Lee.
Application Number | 20100091001 12/585617 |
Document ID | / |
Family ID | 42098441 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100091001 |
Kind Code |
A1 |
Kim; Do-Ik ; et al. |
April 15, 2010 |
Pixel and organic light emitting display device using the same
Abstract
A pixel capable of preventing abnormal light emission thereof. A
pixel includes an organic light emitting diode coupled between a
first power source and a second power source; a pixel circuit unit
having a driving transistor coupled between the first power source
and the organic light emitting diode to supply driving current to
the organic light emitting diode during a light emitting period;
and a bypass unit coupled between the pixel circuit unit and a bias
power source, the bypass unit being turned on during a non-light
emitting period in which the driving transistor is turned off.
Inventors: |
Kim; Do-Ik; (Suwon-si,
KR) ; Lee; Wang-Jo; (Suwon-si, KR) |
Correspondence
Address: |
ROBERT E. BUSHNELL & LAW FIRM
2029 K STREET NW, SUITE 600
WASHINGTON
DC
20006-1004
US
|
Assignee: |
SAMSUNG Mobile Display CO.,
LTD
Yongin-City
KR
|
Family ID: |
42098441 |
Appl. No.: |
12/585617 |
Filed: |
September 18, 2009 |
Current U.S.
Class: |
345/211 ;
345/76 |
Current CPC
Class: |
G09G 2310/0262 20130101;
G09G 2300/0814 20130101; G09G 3/2022 20130101; G09G 3/3225
20130101; G09G 2300/0866 20130101; G09G 2300/0852 20130101 |
Class at
Publication: |
345/211 ;
345/76 |
International
Class: |
G09G 5/00 20060101
G09G005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 2008 |
KR |
10-2008-0100085 |
Claims
1. A pixel, comprising: an organic light emitting diode coupled
between a first power source and a second power source; a pixel
circuit unit having a driving transistor coupled between the first
power source and the organic light emitting diode to supply driving
current to the organic light emitting diode during a light emitting
period; and a bypass unit having a bypass transistor coupled
between the pixel circuit unit and a bias power source, the bypass
transistor being turned on during a non-light emitting period in
which the driving transistor is turned off.
2. The pixel as claimed in claim 1, wherein the bypass transistor
and the driving transistor are set as opposite types of transistors
having gate electrodes coupled to a common node.
3. The pixel as claimed in claim 1, wherein the pixel circuit unit
further comprises: a first switching transistor coupled between a
first node and a data line, the first switching transistor having a
gate electrode coupled to a scan line, the first node being coupled
to a gate electrode of the driving transistor and the data line
through which a data signal is supplied via the first switching
transistor; and a storage capacitor coupled between the first node
and the first power source.
4. The pixel as claimed in claim 3, wherein the bypass unit further
comprises: a second switching transistor coupled between a second
node and an inverted data line, the second switching transistor
having a gate electrode coupled to the scan line, the second node
being coupled to a gate electrode of the bypass transistor and the
inverted data line through which an inverted data signal is
supplied via the second switching transistor; and a control
capacitor coupled between the second node and the first power
source.
5. The pixel as claimed in claim 4, wherein the bypass transistor,
the driving transistor and the first and second switching
transistors are all set as the same type of transistors.
6. The pixel as claimed in claim 4, wherein each of the data signal
and the inverted data signal is supplied as a low or high
level.
7. The pixel as claimed in claim 1, wherein the pixel is digitally
driven by receiving a low-level or high-level first or second data
signal supplied during each of a plurality of sub-frames
constituting one frame.
8. The pixel as claimed in claim 1, wherein the first and second
power sources are set as high-potential and low-potential pixel
power sources, respectively, and the potential of the bias power
source is set lower than that of the second power source.
9. The pixel as claimed in claim 1, wherein the first and second
power sources are set as high-potential and low-potential pixel
power sources, respectively, and the potential of the bias power
source is identical to that of the second power source.
10. An organic light emitting display device, comprising: a pixel
unit having a plurality of pixels formed at intersection areas of
scan and data lines and receiving a first power source, a second
power source and a bias power source from an outside of the organic
light emitting display device; a scan driving unit supplying a scan
signal to the scan lines; and a data driving unit supplying data
signals to the data lines, each of the pixels comprising: an
organic light emitting diode coupled between a first power source
and a second power source; a pixel circuit unit having a driving
transistor coupled between the first power source and the organic
light emitting diode to supply driving current to the organic light
emitting diode during a light emitting period; and a bypass unit
having a bypass transistor coupled between the pixel circuit unit
and a bias power source, the bypass transistor being turned on
during a non-light emitting period in which the driving transistor
is turned off.
11. The organic light emitting display device as claimed in claim
10, wherein the bypass transistor and the driving transistor are
set as opposite types of transistors having gate electrodes coupled
to a same node.
12. The organic light emitting display device as claimed in claim
10, wherein the pixel circuit unit further comprises: a first
switching transistor coupled between a first node and a data line,
the first switching transistor having a gate electrode coupled to a
corresponding scan line, the first node being coupled to the gate
electrode of the driving transistor, and the first node being
coupled to a corresponding data line through which a data signal is
supplied via the first switching transistor; and a storage
capacitor coupled between the first node and the first power
source.
13. The organic light emitting display device as claimed in claim
12, wherein each of the pixels is further coupled to a
corresponding inverted data line through which an inverted data
signal is supplied.
14. The organic light emitting display device as claimed in claim
13, wherein the bypass unit further comprises: a second switching
transistor coupled between a second node and the corresponding
inverted data line, the second switching transistor having a gate
electrode coupled to the corresponding scan line, the second node
being coupled to a gate electrode of the bypass transistor, and the
second node being coupled to the corresponding inverted data line
through which the inverted data signal is supplied via the second
switching transistor; and a control capacitor coupled between the
second node and the first power source.
15. The organic light emitting display device as claimed in claim
14, wherein the bypass transistor, the driving transistor and the
first and second switching transistors are all set as the same type
of transistors.
16. The organic light emitting display device as claimed in claim
10, wherein one frame is divided into a plurality of sub-frames,
the scan driving unit supplies the scan signal to the scan lines
for each of the sub-frames, and the data driving unit supplies
first and second data signals to the data lines for each of the
sub-frames.
17. The organic light emitting display device as claimed in claim
16, wherein the first data signal is set as a voltage level at
which the driving transistor is turned on, the second data signal
is set as a voltage level at which the bypass transistor is turned
on.
18. The organic light emitting display device as claimed in claim
10, wherein the first and second power sources are set as
high-potential and low-potential pixel power sources, respectively,
and the potential of the bias power source is set lower than that
of the second power source.
19. The organic light emitting display device as claimed in claim
10, wherein the bias power source is identical to the second power
source.
Description
CLAIM OF PRIORITY
[0001] This application makes reference to, incorporates the same
herein, and claims all benefits accruing under 35 U.S.C..sctn.119
from an application for PIXEL AND ORGANIC LIGHT EMITTING DISPLAY
DEVICE USING THE SAME earlier filed in the Korean Intellectual
Property Office on 13 Oct. 2008 and there duly assigned Serial No.
10-2008-0100085.
BACK OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a pixel and an organic
light emitting display device using the same, and more
particularly, to a pixel capable of preventing abnormal light
emission, and an organic light emitting display device using the
same.
[0004] 2. Description of Related Art
[0005] An organic light emitting display device is a kind of flat
panel display device which displays images using organic light
emitting diodes that emit light through the recombination of
electrons and holes. The organic light emitting display device has
a fast response speed and is driven with low power consumption.
[0006] Organic light emitting display devices are divided into a
passive matrix type organic light emitting display device (PMOLED)
and an active matrix type organic light emitting display device
(AMOLED) depending on a method of driving an organic light emitting
diode. The AMOLED is used in a portable display device and the like
because of its low power consumption.
[0007] Each pixel of a conventional AMOLED includes an organic
light emitting diode generating light corresponding to an amount of
current supplied to its own pixel; a switching transistor supplying
a data signal into the pixel when a scan signal is supplied; a
storage capacitor storing the data signal from the switching
transistor; and a driving transistor supplying driving current
corresponding to the data signal stored in the storage capacitor to
the organic light emitting diode.
[0008] An ideal pixel does not emit light while cutting off the
flow of current in the pixel, when a data signal that expresses a
black gray scale is supplied. However, an actual pixel emits dim
light due to the leakage current generated from a driving
transistor or the like, when a data signal that expresses a black
gray scale is supplied. As such, when a pixel emits light due to
the leakage current, a contrast ratio is degraded.
SUMMARY OF THE INVENTION
[0009] Accordingly, it is an object of the present invention to
provide a pixel capable of preventing abnormal light emission due
to leakage current, and an organic light emitting display device
using the same.
[0010] According to an aspect of the present invention, there is
provided a pixel including an organic light emitting diode coupled
between a first power source and a second power source; a pixel
circuit unit having a driving transistor coupled between the first
power source and the organic light emitting diode to supply driving
current to the organic light emitting diode during a light emitting
period; and a bypass unit coupled between the pixel circuit unit
and a bias power source, the bypass unit being turned on during a
non-light emitting period in which the driving transistor is turned
off.
[0011] According to another aspect of the present invention, there
is provided an organic light emitting display device, including a
pixel unit having a plurality of pixels formed at intersection
areas of scan and data lines and receiving a first power source, a
second power source and a bias power source from an outside of the
organic light emitting display device; a scan driving unit
supplying a scan signal to the scan lines; and a data driving unit
supplying data signals to the data lines, wherein each of the
pixels comprises: an organic light emitting diode coupled between a
first power source and a second power source; a pixel circuit unit
having a driving transistor coupled between the first power source
and the organic light emitting diode to supply driving current to
the organic light emitting diode during a light emitting period;
and a bypass unit coupled between the pixel circuit unit and a bias
power source, the bypass unit being turned on during a non-light
emitting period in which the driving transistor is turned off.
[0012] According to the present invention, a bypass transistor is
provided to bypass leakage current in a pixel, thereby preventing
abnormal light emission of the pixel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] A more complete appreciation of the invention and many of
the attendant advantages thereof, will be readily apparent as the
same becomes better understood by reference to the following
detailed description when considered in conjunction with the
accompanying drawings in which like reference symbols indicate the
same or similar components, wherein:
[0014] FIG. 1 is a block diagram schematically showing the
configuration of an organic light emitting display device according
to an embodiment of the present invention;
[0015] FIG. 2 illustrates a frame according to the embodiment of
the present invention;
[0016] FIG. 3 is a circuit diagram of a pixel according to an
embodiment of the present invention;
[0017] FIG. 4 is a graph showing voltage-current characteristics;
and
[0018] FIG. 5 is a circuit diagram of a pixel according to another
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Hereinafter, certain exemplary embodiments according to the
present invention will be described with reference to the
accompanying drawings. Here, when a first element is described as
being coupled to a second element, the first element may be not
only directly coupled to the second element but may also be
indirectly coupled to the second element via a third element.
Further, some of the elements that are not essential to the
complete understanding of the invention are omitted for clarity.
Also, like reference numerals refer to like elements
throughout.
[0020] FIG. 1 is a block diagram schematically showing the
configuration of an organic light emitting display device according
to an embodiment of the present invention. FIG. 2 shows a frame
according to the embodiment of the present invention.
[0021] Referring to FIG. 1, the organic light emitting display
device includes a pixel unit 100, a scan driving unit 200, a data
driving unit 300 and a power supply unit 400.
[0022] The pixel unit 100 includes a plurality of pixels 110 formed
at intersection areas of scan lines S1 to Sn and data lines D1 to
Dm. The pixel unit 100 is driven by receiving a first power source
ELVDD, a second power source ELVSS and a bias power source
V.sub.bias supplied from the power supply unit 400.
[0023] The scan driving unit 200 sequentially supplies a scan
signal to the scan lines S1 to Sn in response to a scan control
signal supplied from the outside of the organic light emitting
display device.
[0024] When the organic light emitting display device is driven by
a digital driving method shown in FIG. 2, the scan driving unit 200
supplies a scan signal to the scan lines S1 to Sn during a scan
period of each sub-frame SF. The digital driving method of an
organic light emitting display device is a driving method of
expressing luminance by dividing one frame 1F into a plurality of
sub-frames SFs and setting display periods for the respective
sub-frames SFs to be different.
[0025] When a scan signal is supplied to the scan lines S1 to Sn,
pixels 110 are selected for each line, and the selected pixels 110
receive data signals from the data lines D1 to Dm.
[0026] The data driving unit 300 supplies data signals to the data
lines D1 to Dm in response to data and a data control signal. Then,
the data signals are supplied to the pixels 110 selected by the
scan signal.
[0027] When the organic light emitting display device is driven by
a digital driving method, the data driving unit 300 supplies first
and second data signals to the data lines D1 to Dm as data signals.
Here, the first data signal allows the pixels 110 to emit light,
and the second data signal allows the pixels 110 not to emit light.
The first and second data signals have opposite voltage levels.
[0028] For example, when the first data signal is set as a low
level, the second data signal is set as a high level. That is, the
data driving unit 300 supplies two types of data signals, i.e.,
high and low levels, to the data lines D1 to Dm during a display
period of each of the sub-frames SFs.
[0029] Then, pixels 110 receiving the first data signal emit light
during a predetermined period (a display period of each of the
sub-frames SFs), and pixels 110 receiving the second data signal
supplied from the data driving unit 300 do not emit light, thereby
displaying an image having a predetermined luminance.
[0030] The power supply unit 400 supplies a first power source
ELVDD, a second power source ELVSS and a bias power source
V.sub.bias to the pixel unit 100. Here, the first power source
ELVDD is a high-potential pixel power source, and the second power
source ELVSS is a low-potential pixel power source having a lower
potential than that of the first power source ELVDD. The bias power
source V.sub.bias may be set as a power source having the same
potential as that of the second power source ELVSS. Alternatively,
the bias power source V.sub.bias may be set as a separate power
source having a lower potential than that of the second power
source ELVSS.
[0031] In the organic light emitting display device each of the
pixels 110 has a bypass transistor (not shown) to bypass internal
leakage current generated when each of the pixels 110 does not emit
light. Accordingly, it is possible to prevent abnormal light
emission of the pixels 110, which will be described in detail
later.
[0032] FIG. 3 is a circuit diagram of a pixel according to an
embodiment of the present invention. For convenience of
illustration, FIG. 3 shows a pixel positioned at an n-th row and an
m-th column. The pixel of FIG. 3 may be applied to the organic
light emitting display device shown in FIG. 1.
[0033] Referring to FIG. 3, the pixel 110 includes an organic light
emitting diode OLED coupled between first and second power sources
ELVDD and ELVSS; a pixel circuit unit 112 coupled between the first
power source ELVDD and the organic light emitting diode OLED to
supply a driving current to the organic light emitting diode OLED;
and a bypass unit 114 coupled between the pixel circuit unit 112
and a bias power source V.sub.bias to bypass leakage current
generated from the pixel 110.
[0034] More specifically, an anode electrode of the organic light
emitting diode OLED is coupled to the pixel circuit unit 112, and a
cathode electrode of the organic light emitting diode OLED is
coupled to the second power source ELVSS. The organic light
emitting diode OLED emits light in response to current supplied
from the pixel circuit unit 112.
[0035] The pixel circuit unit 112 includes a driving transistor DT,
a switching transistor ST1 and a storage capacitor Cst.
[0036] The driving transistor DT is coupled between the first power
source ELVDD and the anode of the organic light emitting diode
OLED, and a gate electrode of the driving transistor DT is coupled
to a first node N1. A storage capacitor Cst is coupled between the
first node N1 and the first power source ELVDD. The driving
transistor DT supplies driving current to the organic light
emitting diode OLED in response to a voltage at the first node N1.
A gate electrode of the bypass transistor BT is also coupled to the
first node N1.
[0037] In the pixel driven by the digital driving method, the
driving transistor DT supplies or does not supply driving current
to the organic light emitting diode OLED in response to a low-level
or high-level data signal Vdata supplied during a period of each of
the sub-frames SFs. Here, the low-level data signal Vdata (a first
data signal) is set as a voltage level capable of allowing the
driving transistor DT to be turned on and allowing the bypass
transistor BT to be turned off The high-level data signal Vdata (a
second data signal) is set as a voltage level capable of allowing
the driving transistor DT to be turned off and allowing the bypass
transistor BT to be turned on.
[0038] For example, when the low-level data signal Vdata is
supplied to the first node N1 through a data line Dm, the driving
transistor DT is turned on and supplies driving current to the
organic light emitting diode OLED. When the high-level data signal
Vdata is supplied to the first node through the data line Dm, the
driving transistor DT is turned off and does not supply driving
current to the organic light emitting diode OLED.
[0039] Hereinafter, the display period in which the organic light
emitting diode OLED is turned on is referred to as a "light
emitting period," and the period in which the driving transistor DT
is turned off is referred to as a "non-light emitting period."
[0040] That is, when the first data signal (low-level data signal)
is supplied in a corresponding sub-frame SF, the driving current is
supplied to the organic light emitting diode OLED by the turned-on
driving transistor DT so that the organic light emitting diode OLED
emits light. When the second data signal (high-level data signal)
is supplied in the corresponding sub-frame SF, the driving current
is not supplied to the organic light emitting diode OLED by the
turned-off driving transistor DT so that the organic light emitting
diode OLED does not emit light.
[0041] The switching transistor ST1 is coupled between the first
node N1 and the data line Dm, and a gate electrode of the switching
transistor ST1 is coupled to a scan line Sn. When a scan signal SS
is supplied to the switching transistor ST1 through the scan line
Sn, the switching transistor ST1 is turned on to transfer the data
signal Vdata supplied from the data line Dm to the first node
N1.
[0042] The storage capacitor Cst is coupled between the first node
N1 and the first power source ELVDD. Here, when the data signal
Vdata is supplied to the first node N1, a voltage corresponding to
the data signal Vdata is charged into the storage capacitor Cst.
That is, when the organic light emitting display device is driven
by a digital driving method, the data signal Vdata supplied for
each of the sub-frames SFs is charged into the storage capacitor
Cst, and the storage capacitor Cst maintains the voltage at the
first node N1 during a corresponding sub-frame SF.
[0043] The bypass unit 114 is coupled between the pixel circuit
unit 112 and the bias power source V.sub.bias. The bypass unit 114
includes a bypass transistor BT which may coupled in parallel with
the organic light emitting diode OLED when the second power source
ELVSS and the bias power source V.sub.bias are identical. In order
to bypass leakage current to the bias power source V.sub.bias, the
potential of the bias power source V.sub.bias may be set lower than
that of the second power source ELVSS.
[0044] More specifically, the bypass transistor BT is coupled
between the driving transistor DT and the bias power source
V.sub.bias. The bypass transistor BT is turned on during the
non-light emitting period in which the driving transistor DT is
turned off, to bypass leakage current generated in the pixel 110 to
the bias power source V.sub.bias.
[0045] To this end, in this embodiment, a gate electrode of the
bypass transistor BT is coupled to the first node N1 coupled to the
gate electrode of the driving transistor DT, but the bypass
transistor BT and the driving transistor DT are set as opposite
types of transistors. For example, when the driving transistor DT
is set as a p-type transistor, the bypass transistor BT is set as
an n-type transistor.
[0046] Accordingly, when the organic light emitting display device
is driven by a digital driving method, the bypass transistor BT is
turned off during the light emitting period in which the first data
signal is supplied, and the bypass transistor BT is turned on
during the non-light emitting period in which the second data
signal is supplied. As such, when the bypass transistor BT is
turned on during the non-light emitting period, leakage current is
bypassed through the bypass transistor BT, so that the leakage
current does not flow through the organic light emitting diode
OLED. Here, the leakage current may be generated related to
characteristics of the driving transistor DT, a crosstalk or a
charge discharge of the storage capacitor Cst. Accordingly, it is
possible to prevent abnormal light emission of the organic light
emitting diode OLED during the non-light emitting period.
[0047] The operation of the aforementioned pixel 110 will now be
described. When a scan signal SS is supplied to the switching
transistor ST1 through the scan line Sn, the switching transistor
ST1 is first turned on. Then, a data signal Vdata supplied from the
data line Dm to the first node N1. At this time, a voltage
corresponding to the data signal Vdata is charged into the storage
capacitor Cst.
[0048] When the data signal Vdata is a low-level first data signal,
the driving transistor is turned on and the bypass transistor BT is
turned off. Accordingly, driving current flows between the first
power source ELVDD and the second power source ELVSS via the
driving transistor DT and the organic light emitting diode OLED, so
that the organic light emitting diode OLED emits light.
[0049] When the data signal Vdata is a high-level second data
signal, the driving transistor DT is turned off and the bypass
transistor BT is turned on. Then, driving current is not supplied
from the driving transistor DT to the organic light emitting diode
OLED, and leakage current which may be generated from the driving'
transistor DT is bypassed to the bias power source V.sub.bias
through the bypass transistor BT.
[0050] When leakage current occurs from the driving transistor DT,
a voltage V.sub.oled to the organic light emitting diode OLED is
determined by a ratio of off-resistance of the driving transistor
DT to on-resistance of the bypass transistor BT. Although
characteristics of the driving transistor DT are not excellent as a
resistance ratio of 100:1 or so, a low voltage of below a few tens
of mV is applied to the organic light emitting diode OLED.
[0051] Here, a very low current I.sub.oled close to zero flows
through the organic light emitting diode OLED in an area where a
low voltage V.sub.oled is applied the organic light emitting diode
OLED as shown in area A of FIG. 4. Therefore, current hardly flows
through the organic light emitting diode OLED at a low voltage
V.sub.led. Accordingly, a non-light emitting state is maintained in
the organic light emitting diode OLED by the turned-on bypass
transistor BT during the non-light emitting period.
[0052] In order to bypass leakage current to the bias power source
V.sub.bias, the potential of the bias power source V.sub.bias may
be set lower than that of the second power source ELVSS.
[0053] When the potential of the bias power source V.sub.bias is
identical to that of the second power source ELVSS, the second
power source ELVSS may be used as the bias power source V.sub.bias
without supplying a separate power source. At this time, the
voltage difference between the anode and cathode electrodes of the
organic light emitting diode OLED becomes zero during the non-light
emitting period. Therefore, an off-state is maintained in the
organic light emitting diode OLED.
[0054] When the potential of the bias power source V.sub.bias is
lower than that of the second power source ELVSS, a reverse voltage
is applied to the organic light emitting diode OLED during the
non-light emitting period. Therefore, the lifespan of the organic
light emitting diode OLED is extended.
[0055] FIG. 5 is a circuit diagram of a pixel according to another
embodiment of the present invention. In FIG. 5, elements identical
to those of FIG. 3 are designated by same reference numerals, and
their detailed descriptions will be omitted.
[0056] Referring to FIG. 5, the pixel 110' is further coupled to an
inverted data line INDm through which an inverted data signal Vdata
is supplied. In this case, in the organic light emitting display
device of FIG. 1, an inverted data line INDm may be further added
to each channel of the data driving unit 300 corresponding to a
data line Dm. Alternatively, a separate circuit may be provided
between the data driving unit 300 and the pixel unit 100 or in the
pixel unit 100. Here, the separate circuit inverts data signals and
supplied them to the pixels 110.
[0057] Like the bypass transistor BT of FIG. 3, a bypass transistor
BT' may be coupled in parallel with an organic light emitting diode
OLED between a driving transistor DT and a bias power source
V.sub.bias, an when the second power source ELVSS and the bias
power source V.sub.bias are identical. A gate electrode of the
bypass transistor BT' is coupled to a second node N2.
[0058] A bypass unit 114' includes bypass transistor BT', second
node N2 and further includes a switching transistor ST2 and a
control capacitor Cc. The switching transistor ST2 is coupled
between the inverted data line INDm and the second node N2, and a
gate electrode of the switching transistor ST2 is coupled to a scan
line Sn. The control capacitor Cc is coupled between the second
node N2 and first power source ELVDD.
[0059] When a scan signal SS is supplied to the scan line Sn, the
switching transistor ST2 is turned on to supply the inverted data
signal Vdata supplied through the inverted data line INDm to the
second node N2. At this time, a voltage corresponding to the
inverted data signal Vdata is charged into the control capacitor
Cc.
[0060] The operation of the aforementioned pixel 110' will now be
described. When a scan signal SS is supplied to the scan line Sn,
the first and second transistors ST1 and ST2 are first turned on.
Then, a data signal Vdata supplied through the data line Dm is
supplied to a first node N1, and an inverted data signal Vdata
supplied through the inverted data line INDm is supplied to the
second node N2. At this time, a voltage corresponding to the data
signal Vdata is charged into a storage capacitor Cst, and a voltage
corresponding to the inverted data signal Vdata is charged into the
control capacitor Cc.
[0061] When the data signal Vdata is a low-level first data signal
and the inverted data signal Vdata is a high-level second data
signal, the driving transistor DT is turned on, and the bypass
transistor BT' is turned off. Accordingly, driving current flows
from the first power source ELVDD to a second power source ELVSS
via the driving transistor DT and the organic light emitting diode
OLED, so that the organic light emitting diode OLED emits
light.
[0062] When the data signal Vdata is a high-level second data
signal and the inverted data signal Vdata is a low-level second
data signal, the driving transistor DT is turned off, and the
bypass transistor BT' is turned on. Then, driving current is not
supplied from the driving transistor DT to the organic light
emitting diode OLED, and leakage current which may be generated
from the driving transistor DT is bypassed to the bias power source
V.sub.bias through the bypass transistor BT. Accordingly, a
non-light emitting state is maintained in the organic light
emitting diode OLED by the turned-on bypass transistor BT during
the non-light emitting period.
[0063] Meanwhile, in this embodiment, the driving transistor DT,
the bypass transistor BT' and the first and second switching
transistors ST1 and ST2 are all set as the same type of
transistors. For example, the driving transistor DT, the bypass
transistor BT' and the first and second switching transistors ST1
and ST2 may all be set as p-type transistors. Accordingly, a
process of forming the pixel 110' can be simplified not by using a
CMOS process but by using a relatively small number of masks.
[0064] Although the transistors of the pixel 110' in FIG. 5 are all
set as p-type transistors, the present invention is not limited
thereto. For example, it will be apparent that the present
invention may be implemented by setting all the transistors in the
pixel 110' as n-type transistors and modifying a circuit
configuration to be suitable for the n-type transistors.
[0065] While the present invention has been described in connection
with certain exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed embodiments, but, on the
contrary, is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended
claims, and equivalents thereof.
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